Robotic manipulator impedance control of generalized contact force and position

Robotic manipulator impedance control has been presented as a control methodology with the philosophy that a manipulator control system should be designed, not to track a particular motion or force trajectory alone, but rather to regulate the interaction between force and motion. Regulation of generalized contact force and generalized position of the manipulator has not yet been addressed through the use of impedance controllers, as initially proposed in the literature. In this paper, a method is proposed, using an impedance control not only to regulate the interaction between manipulator generalized force and position, but importantly, to additionally control the generalized contact force and position. An algorithm is proposed which determines the appropriate manipulator generalized position inputs, the only input signal available to an impedance control, in order to generate specific generalized force and position trajectories. This goal is achieved while independently regulating the interaction between manipulator force and position. In this paper, the manipulator is assumed to be a rigid structure in frictionless point contact with a work environment modelled as a general linear mechanical impedance. The stability of the robotic manipulator during object contact, implicitly assumed by the proposed control strategy, is established using the theory of singular perturbations. Experimental results obtained with a two degree of freedom direct drive manipulator during contact with a one degre of freedom linear mechanical impedance illustrate the usefulness of the proposed method